In order for airplanes to be efficiently utilized, they must be capable of flying in a variety of weather conditions. When the weather is good, an airplane can be flown by a pilot with reference only to what the pilot can see out the windows. That is, a pilot can judge turns, climbs, descents and direction by observing visual references, such as the position of the horizon and the sun. However, when the weather degrades so that these external visual references can no longer be accurately relied upon, the pilot must rely on other indicators of the attitude of his airplane.
When external visual references outside the airplane are obscured, the normal senses, such as the sense of balance provided by the inner ear, can be fooled. Without visual references, a pilot relying on his other sense might believe his plane is in a climb when in fact the plane is in a steep bank.
To overcome these problems, flight instruments were developed to provide a pilot with visual indications of the airplane's attitude. Although the type of flight instruments and their arrangement on the instrument panel vary considerably from airplane to airplane, there are certain basic instruments which are typically found in virtually all airplanes. The most frequent arrangement of instruments is referred to as the "Basic T." The central instrument in this arrangement is an artificial horizon or attitude gyro. This instrument usually comprises a card with a black face and a white horizon line on it. The card is attached to a gyro. A minature airplane is attached to the cage so that the artificial horizon moves with respect to the miniature airplane in the same manner as the real airplane moves with respect to the real horizon.
Immediately below the artificial horizon is the heading indicator or directional gyro. This instrument comprises a compass card or an azimuth scale attached to a gyro. The gyro fixes the compass card in space so that the airplane turns around the compass card. The directional gyro performs essentially the same function as a magnetic compass, that is, it provides information about the directional heading of the airplane.
To the right of the artificial horizon is an altimeter. The altimeter interprets changes in air pressure as an airplane climbs or descends, to provide information about the altitude of the airplane.
To the left of the artificial horizon is an air speed indicator. The air speed indicator detects the pressure of the air impacting an external pilot tube as the airplane moves forward through the air. This pressure is converted to give a reading of the relative speed of the airplane with respect to the air through which it is flying.
These four instruments make up the "Basic T." Two other instruments, however, are usually included in addition to these "basic" instruments. To the right of the directional gyro is a vertical speed indicator. This instrument detects the rate of change of air pressure to give indications of how fast an airplane is climbing or descending.
To the left of the directional gyro is a turn and slip indicator. This instrument is actually two instruments in one. The slip indicator is a curved glass tube with a ball inside it. The ball will remain at the bottom of the glass tube when the forces acting on it are balanced; for example, when the plane is in straight and level flight or in a coordinated turn. When the airplane is in a slip or a skid the forces will not be balanced and the ball will be displaced. The turn indicator is another gyro instrument. A needle detects precession of the gyro to give indications of the direction and rate of a turn of the airplane.
Although variations of these instruments will be found in different airplanes, they will usually all be found in the instrument panel in one form or another. With the aid of one or more of these instruments an airplane can be flown without external visual reference.
It is a typical problem when learning to fly an airplane by instruments that the pilot will fixate on only one instrument. This causes him to ignore other instruments which might be giving indications that are important to maintaining the proper flight attitude of the airplane. Accordingly, it is generally recognized that it is essential for a pilot to scan the instruments to thereby prevent fixation and to be fully aware of all the information which is essential to maintain safe flight of the airplane. It is not, however, necessary that the pilot scan all six instruments at all times. For various airplane maneuvers, such as a standard rate turn at constant altitude or straight and level flight, it is critical that only certain instruments be scanned. It is therefore possible to establish scanning patterns for various flight maneuvers.
Although books describe these scanning patterns, heretofore there has not been an effective visual training aid for the learning of flight instrument scanning.